JP7555208B2 - Large hollow porous quartz glass base material and its manufacturing method - Google Patents

Description

The present invention relates to a large hollow porous quartz glass base material and its manufacturing method, as well as a hollow synthetic quartz glass cylinder using the same and its manufacturing method, and in particular to a large heavy hollow porous quartz glass base material with an outer diameter exceeding 300 mm, a manufacturing method for a hollow porous quartz glass base material that can suitably manufacture the large hollow porous quartz glass base material, and a hollow synthetic quartz glass cylinder using the same and its manufacturing method.

Synthetic quartz glass is widely used in the optical, semiconductor and chemical industries, particularly as a lens material for projection and exposure systems in microlithography, as well as in semiconductor manufacturing tools and optical fiber materials.

The manufacture of hollow synthetic quartz glass cylinders generally involves manufacturing a hollow porous synthetic quartz glass base material (soot body) and sintering it to make it transparent. The OVD method (Outside Vapor Deposition) is known for manufacturing soot bodies, and the soot body is manufactured by converting silicon-containing raw material into fine _SiO2 particles by flame hydrolysis or pyrolysis and depositing them on the outer surface of a target rotating around its long axis.

The hollow porous quartz glass base material (soot body) requires the removal of the target before sintering, and this is done by rotating the target and hollow soot body relative to one another and moving them in the longitudinal direction. This is extremely difficult if the soot body and the target are stuck together. Furthermore, even if it is possible to remove the target by applying a large force, scratches will be created on the inside of the soot body during the process, and these scratches will remain as localized defects in the quartz cylinder after sintering, resulting in defective parts.

In recent years, the demand for larger quartz cylinders has increased due to the increasing diameter of semiconductor wafers and the increasing size of optical fiber base materials. In order to manufacture large quartz cylinders, the hollow porous quartz glass base material (soot body), which is an intermediate product in the manufacturing process, must also be made larger and heavier. However, as the soot body becomes heavier and heavier, there is a problem that the task of extracting the target from the soot body becomes difficult. This means that it is difficult to achieve both: the target and soot body are integrated during soot body growth, and the soot body rotates following the target, and the target can be extracted from the soot body after soot growth.

In the OVD method, multiple burners for synthesizing glass particles are arranged at regular intervals, and the row of burners is moved back and forth (swinged) relative to a rotating starting member (target) to deposit glass particles in layers on the target, resulting in a soot body. At the turning point of the swing, the swing speed momentarily becomes zero, so the time during which the flame is actually irradiated is longer than in the part swinging at a steady speed. As a result, the amount of glass particles deposited at the turning point is large, and unevenness occurs in the longitudinal direction. For this reason, Patent Document 1 describes a traverse method in which the turning point of the swing is moved a specified distance at a time in order to distribute the deposition in the longitudinal direction, thereby obtaining a soot body with a uniform outer diameter in the longitudinal direction, and this traverse method is well known as a method for distributing the deposition amount and density distribution.

In addition, in the OVD method, deposition is performed on the outer surface of the target while rotating it around its long axis. Therefore, if the rotation speed of the soot body is constant, the peripheral speed of the outer surface of the soot body increases as the outer diameter of the soot body grows, and the irradiation time per unit area becomes shorter, making it impossible to obtain a radially homogeneous soot body. Recently, as the diameter and thickness of soot bodies are becoming larger in order to improve productivity and reduce costs, the effect is particularly noticeable for large-diameter soot bodies with outer diameters exceeding 300 mm, and it is necessary to control the rotation speed to be lower as the outer diameter of the soot body grows so that the peripheral speed is constant. Furthermore, even if the peripheral speed is constant, if the speed is faster than a certain level, vibrations will occur due to slight eccentricity of the radial center of gravity when the outer diameter becomes large in the later growth stage, and the load on the rotating device will increase, making stable production impossible. Furthermore, if the peripheral speed is faster than a certain level, the soot body will not follow the rotation of the target and will spin freely at the interface between the soot body and the target, causing the soot body to be unable to rotate stably at a constant speed. This problem can be avoided by strengthening the adhesion of the soot body to the target, but in that case the target extraction work described above becomes extremely difficult, and even if the target can be extracted, localized defects will occur. For this reason, a constant peripheral speed at a low rotation speed is essential.

However, when the size was increased and low rotation conditions were used to keep the peripheral speed constant, cracks and ruptures frequently occurred during or after growth was completed. Even if it did not reach that stage, if treatment with a chlorinating agent was performed, the chlorine concentration distribution of the synthetic quartz glass cylinder after sintering became non-uniform, and if treatment with a chlorinating agent was not performed, the OH group concentration distribution became non-uniform, making it impossible to obtain a quartz glass cylinder with optically homogeneous physical properties.

In the manufacture of optical fibers, the difference in chlorine concentration in the radial and circumferential directions is important, and recent research has revealed that fiber curl is improved by reducing the difference in chlorine concentration distribution in the circumferential direction in particular. When drawing large-diameter preforms, the amount of drawing per unit length increases and the deformation time in the drawing furnace increases, which causes the local homogeneity of the cladding to affect the properties of the fiber. Therefore, as the size of the cladding glass base material increases, stability of the chlorine concentration over a smaller range becomes important.

Quartz glass cylinders manufactured without chlorination are often used as the raw material for quartz glass jigs and lamps used in semiconductor manufacturing equipment. To obtain such quartz glass material, it is molded and heat processed to the desired size, but if there is a large difference in OH group concentration during this process, a viscosity distribution will occur within the cylinder, resulting in shape instability problems such as uneven thickness, siding, and ovality. As with the optical fiber mentioned above, this becomes more noticeable as the glass size increases, so it is important to stabilize the OH group concentration over a small area.

Regarding the reciprocating motion of the burner and the rotation of the support in the OVD method, Patent Document 2 describes that the base temperature of the surface is maintained between 1050°C and 1350°C, the average peripheral speed is maintained between 8 m/min and 15 m/min, and the translation speed (swing speed) of the burner row is maintained between 300 mm/min and 800 mm/min, thereby enabling the production of a base material with almost no local axial density fluctuation. However, in the method described in Patent Document 2, for example, if the swing distance is 100 mm, the swing speed is 800 mm/min, and the average peripheral speed is 9 m/min, the rotation speed needs to be increased from 19.1 rpm to 6.4 rpm to grow the outer diameter (hereinafter, the outer diameter is also referred to as OD) of the deposit from 100 mm to 300 mm. However, if production is performed under these conditions, cracks will occur during growth and growth cannot continue.

Furthermore, Patent Document 3 describes a method in which the turning point of the reciprocating motion is moved in a fixed direction by a specified distance and then moved in the opposite direction at a specified position, in which the rotation speed is kept constant and conditions are set to satisfy the following relationship, thereby suppressing external shape fluctuations (axial unevenness of the soot).
The value represented by A = (r/v) x L is 40 ≥ A ≥ 8
[r = rotation speed (rpm), v = reciprocating speed (mm/min), L = burner spacing]

In the method described in Patent Document 3, for example, when the swing speed is 850 mm/min and the swing width is 100 mm, the rotation speed r (rpm) must be set to 68≦r≦320 in order to set A within the specified range. However, when the outer diameter of the deposition body is large, for example, when the OD is 300 mm, the surface peripheral speed p (m/min) is fast at 64≦p≦301, and a strong centrifugal force is generated. The force increases as the weight and diameter increase, so vibration occurs, and the device and target must be made rigid enough to withstand the centrifugal force, which makes them expensive, and there is also a problem that cracks occur during growth. Furthermore, Patent Document 3 is a method of depositing silica glass particles on the surface of a starting rod to manufacture a solid optical fiber preform, but it is not a method of manufacturing a hollow porous silica glass base material. In the method described in Patent Document 3, in order to manufacture a soot body with an outer diameter of 300 mm or more without freewheeling between the interface of the target, it is necessary to firmly fix the target and the soot body, but in such a case, there is also a problem that it is difficult to extract the target.

Patent Document 4 also describes that fluctuations in the longitudinal diameter are suppressed by setting the reciprocating movement speed (swing speed) and rotation speed so that the rotational position of the starting rod is shifted by half a period from its original position when the relative reciprocating movement (swing) of the starting rod and the burner makes one round trip and returns to its original position, and describes the following conditions.
(L/V)×N(rpm)=n+0.5±0.1
[L = moving distance (mm), V = reciprocating speed (mm/min), N = number of rotations of the rod (rpm), n: any integer]

In the method described in Patent Document 4, the rotational position is shifted by 0.5 rotational periods (180°) when the rod goes back and forth once, so when the rod goes back and forth twice, the rotational position is shifted by one rotation (360°). For example, when the swing speed is 850 mm/min and the swing width is 100 mm, the above formula is satisfied when the rotation speed is 12.75 rpm (100 mm/850 mm/min x 12.75 rpm = 1.5). However, in the case of 12.75 rpm, the timing of the swing turnaround position and one rotation coincides once every three rotations, and a density distribution is formed in the soot body in both the long axis direction and the radial direction. Furthermore, Patent Document 4 is also a method of depositing glass particles on the surface of a starting rod to produce a solid glass particle deposition body, but it is not a method of producing a hollow porous quartz glass base material.

As mentioned above, none of the patent documents discloses the local density distribution of the soot body under low rotation speed conditions that allows the extraction of a target from a large soot body with an outer diameter exceeding 300 mm, and does not disclose an invention that solves this problem to suppress the occurrence of cracks.

Japanese Patent Application Publication No. 3-228845 Special Publication No. 2001-504426 JP 2002-167228 A JP 2013-43810 A

The present invention aims to provide a large hollow synthetic quartz glass porous base material and a manufacturing method thereof, as well as a hollow synthetic quartz glass cylinder and a manufacturing method thereof, which can produce a soot body without significantly increasing the load on the device, such as centrifugal force generated during growth, even when the soot body has an outer diameter of more than 300 mm, and which eliminates the local density distribution of the soot body under constant low peripheral speed conditions that accompany the increase in the diameter of the soot body when the outer diameter exceeds 300 mm, and which does not cause cracks or ruptures in the soot body even when produced at a low rotation speed, and which makes it easy to extract a target from the increased diameter soot body.

In order to solve the above problem, the soot body was investigated and it was found that there is a difference not only in the amount of deposition but also in the density of the deposited layer at the turning point of the reciprocating movement of the burner in the soot body. In this invention, the reciprocating movement of the burner is called a swing. Figure 4 is a graph showing the turning point of the reciprocating movement (swing) of the burner and the density distribution of the deposited layer in the longitudinal direction of the soot body. As shown in Figure 4, at the turning point of the burner, the density is higher than when the swing speed is moving at a steady speed, and repeated deposition generates an axial density distribution in the soot body.

Further investigation revealed that the density difference was formed not only in the axial direction but also in the radial direction locally. A detailed analysis of the local density variation in the radial direction revealed that the timing occurred when the swing turning point and one rotation coincided. Figure 5 is a graph showing the density distribution in the radial direction of the soot body. As shown in Figure 5, the swing turning point where the density is high is usually distributed in the circumferential direction, but when the swing turning point and one rotation timing coincide and the soot body grows for a certain period of time or more, the high density area does not distribute, and the high density area and the low density area overlap in the circumferential direction, and it was found that there are areas where the density is extremely low. In Figure 5, γ is a frequency coefficient calculated by the following formula (1).
γ=S/(L・N _m )...(1)
[In the above formula (1), S is the burner moving speed (mm/min), L is the burner moving distance (mm), and _Nm is the minimum value (rpm) at which the soot body fluctuates.]

In other words, it was found that not only the deposition amount and density distribution in the axial direction in the soot body but also local density distribution occurs in the radial direction, which causes various problems such as cracks, chlorine concentration distribution, and OH group concentration distribution. Furthermore, it was found that by controlling the rotational speed of the soot body during growth to be practically constant and setting the frequency coefficient γ to be within a predetermined range, it is possible to create a soot body even with an outer diameter of more than 300 mm without significantly increasing the load on the device, such as the centrifugal force generated during growth, and further to suppress the occurrence of cracks and to suppress non-uniformity in the chlorine concentration and OH group concentration. Furthermore, it was found that the above settings make it possible to easily extract a target from a large-diameter soot body.

That is, the method for producing a hollow porous quartz glass base material of the present invention includes the steps of arranging a plurality of burners for synthesizing glass particles at a predetermined interval, moving the burners back and forth, and depositing glass particles on a rotating target to grow a soot body, and extracting the target from the soot body to produce a hollow porous quartz glass base material, and is characterized in that the rotational peripheral speed of the soot body is controlled to be essentially constant by varying the rotation speed of the soot body based on the outer diameter of the soot body which varies during growth, and the frequency coefficient γ calculated by the following formula (1) is set to be in the range of the following formula (2) in the range where the outer diameter of the soot body exceeds 250 mm.
γ=S/(L・N _m )...(1)
0.13≦γ<1.0 (2)
[In the formula (1), S is the moving speed of the burner (mm/min), L is the moving distance of the burner (mm), and _Nm is the minimum value (rpm) of the fluctuating rotation speed of the soot body.]

When performing the wobbling under conditions in which the turning position in the reciprocating movement of the burner is moved by a predetermined distance, it is preferable to set it so that it falls within the range of the above formula (2) when the amount of movement of the turning position in one reciprocating movement of the burner is 1/3 or less of the flame diameter of the burner irradiated to the soot body. In the present invention, moving the turning position in the reciprocating movement of the burner by a predetermined distance is called wobbling. In the method of the present invention, by performing wobbling under the above conditions, it is possible to obtain a homogeneous hollow porous quartz glass base material with an extremely small density fluctuation. Note that, under wobbling conditions, if the amount of movement of the turning position exceeds 1/3 of the flame diameter, the turning positions are dispersed, so heat is also dispersed, and problems such as cracks and non-uniform physical properties are relatively unlikely to occur.

It is preferable that the frequency coefficient γ is 0.13 or more and 0.3 or less. By setting the frequency coefficient γ to 0.3 or less, it is possible to obtain a hollow synthetic quartz glass cylinder that is free of cracks or ruptures in the soot body, has a uniform distribution of the chlorine content concentration and the OH group content concentration, and is extremely homogeneous in terms of optical and thermal properties.

The method for manufacturing a synthetic quartz glass cylinder of the present invention is characterized by using a hollow porous quartz glass base material obtained by the method for manufacturing a hollow porous quartz glass base material of the present invention.

A first embodiment of the hollow porous quartz glass base material of the present invention is a large cylindrical hollow porous quartz glass base material having an outer diameter exceeding 300 mm and a length of 2 m or more, characterized in that the average density of the entire base material is 0.55 g/cm3 or ^more , the density variation per unit length at four points equidistant from the inner surface in the radial direction in four directions every 90° on the cylindrical cross section is 10%/cm or less compared to the average value of the four points, and the base material is free of cracks.

A second embodiment of the hollow porous quartz glass base material of the present invention is a large cylindrical hollow porous quartz glass base material having an outer diameter of 500 mm or more and a length of 1.0 m or more, characterized in that the average density of the entire base material is 0.55 g/cm3 or ^more , the density variation per unit length at four points equidistant from the inner surface in the radial direction in four directions every 90° on the cylindrical cross section is 10%/cm or less compared to the average value of the four points, and the base material is free of cracks.

The large-sized hollow porous quartz glass base material is preferably obtained by the manufacturing method for the hollow porous quartz glass base material.

The third aspect of the hollow porous quartz glass base material of the present invention is a hollow porous quartz glass base material obtained by the manufacturing method of the hollow porous quartz glass base material, which is manufactured under the above-mentioned wobbling conditions and under conditions in which the movement amount of the turning position in one round trip of the burner is less than 1/3 of the flame diameter of the burner irradiated to the soot body, and is characterized in that the density variation per unit length at four points equidistant from the inner surface in the radial direction in four directions every 90° on the cylindrical cross section is 2%/cm or less compared to the average value of the four points.

The first embodiment of the hollow synthetic quartz glass cylinder of the present invention is obtained by dehydrating and vitrifying the hollow porous quartz glass base material, and is characterized by having an outer diameter of 200 to 500 mm, a length of 0.7 to 3.5 m, an OH group concentration of less than 5 ppm, and a chlorine concentration of 500 ppm to 3000 ppm, and being free of external appearance defects caused by cracks in the porous member.

In the first embodiment of the hollow synthetic quartz glass cylinder, it is preferable that the "maximum-minimum difference" of the chlorine concentration at four positions equidistant from the inner surface of the cylindrical cross section of the hollow synthetic quartz glass cylinder, spaced every 90° in the circumferential direction, is within 15% of the average value of the four positions.

The second embodiment of the hollow synthetic quartz glass cylinder of the present invention is obtained by pre-sintering and vitrifying the hollow porous quartz glass base material, and is characterized in that it has an outer diameter of 200 to 500 mm, a length of 0.7 m to 3.5 m, an OH group concentration of 50 ppm to 500 ppm, and is free of external defects caused by cracks in the porous member.

In the second embodiment of the hollow synthetic quartz glass cylinder, it is preferable that the "maximum-minimum difference" of the OH group concentration at four positions every 90° in the circumferential direction that are equidistant from the inner surface of the cylindrical cross section of the hollow synthetic quartz glass cylinder is within 15% of the average value of the four positions.

The third embodiment of the hollow synthetic quartz glass cylinder of the present invention is a hollow synthetic quartz glass cylinder obtained by vitrifying the third embodiment of the hollow porous quartz glass base material, characterized in that the "maximum-minimum difference" of the chlorine concentration at four positions equidistant from the inner surface of the cylindrical cross section of the hollow synthetic quartz glass cylinder, spaced every 90° in the circumferential direction, is 10% or less of the average value of the four positions.

The fourth aspect of the hollow synthetic quartz glass cylinder of the present invention is a hollow synthetic quartz glass cylinder obtained by vitrifying the hollow porous quartz glass base material of the third aspect, characterized in that the "maximum-minimum difference" of the OH group concentration at four positions equidistant from the inner surface of the cylindrical cross section of the hollow synthetic quartz glass cylinder, spaced every 90° in the circumferential direction, is 10% or less of the average value of the four positions.

According to the present invention, even if the soot body has an outer diameter of more than 300 mm, it is possible to create a soot body without significantly increasing the load on the apparatus, such as centrifugal force generated during growth, and further, it is possible to eliminate the local density distribution of the soot body under constant peripheral speed and low rotation speed conditions that accompanies the increase in the diameter of the soot body exceeding 300 mm, and to provide a large hollow synthetic quartz glass porous base material and a manufacturing method thereof, as well as a hollow synthetic quartz glass cylinder and a manufacturing method thereof, which are significant in that they are capable of eliminating cracks or ruptures in the soot body even when produced at low rotation speeds, and which facilitate the extraction of a target from the increased diameter soot body.
Furthermore, according to the present invention, it is possible to obtain a large hollow synthetic quartz glass cylinder having a uniform chlorine content or OH group content and extremely homogeneous optical and thermal properties.

FIG. 1 is a schematic diagram illustrating a method for producing a hollow porous quartz glass base material according to the present invention. 1A and 1B are schematic explanatory diagrams showing the movement of a burner in a method for producing a hollow porous quartz glass base material of the present invention, where (a) shows a non-wobbling condition and (b) shows a wobbling condition. FIG. 2 is a schematic explanatory diagram showing burner irradiation in the method for producing a hollow porous quartz glass base material of the present invention. 1 is a graph showing the turning point of the reciprocating movement of a burner and the density distribution of a deposited layer in the longitudinal direction of a soot body. 1 is a graph showing a density distribution in a radial direction of a soot body. FIG. 2 is a schematic diagram showing a method for measuring the density of the hollow porous quartz glass base material of the present invention.

The following describes embodiments of the present invention, but these embodiments are shown as examples, and it goes without saying that various modifications are possible without departing from the technical concept of the present invention. In the drawings, the same members are denoted by the same reference numerals.

1 is a schematic diagram showing the method for producing a hollow porous quartz glass base material of the present invention. The method for producing a hollow porous quartz glass base material of the present invention is a method for producing a hollow porous quartz glass base material by arranging a plurality of glass particle synthesis burners 16a, reciprocating the burners 16a, depositing glass particles on a rotating target 14, and growing a soot body 12, and controlling the rotational speed of the soot body 12 to be practically constant by varying the rotation speed of the soot body 12 based on the outer diameter of the soot body 12 that varies during growth, and setting the frequency coefficient γ calculated by the following formula (1) to be within the range of the following formula (2) when the outer diameter of the soot body exceeds 250 mm. Note that practically constant means ±5%.
γ=S/(L・N _m )...(1)
0.13≦γ<1.0 (2)
[In the formula (1), S is the moving speed (mm/min) of the burner 16a, L is the moving distance (mm) of the burner 16a, and _Nm is the minimum value (rpm) of the fluctuating rotation speed of the soot body 12.]

In FIG. 1, reference numeral 10 denotes a manufacturing device for producing a hollow porous quartz glass base material, and includes a target holding and rotating mechanism 20 that rotates and holds a target 14 and controls the rotation speed (rpm), a glass particle synthesis burner group 16 in which multiple glass particle synthesis burners 16a are arranged at predetermined intervals, and a burner group movement control device 18 that controls the swing and vertical movement of the burner group 16.

As shown in FIG. 1, a target holding and rotating mechanism 20 that controls the rotation speed of the target 14 and a group of glass particle synthesis burners 16 whose swing (reciprocating movement) and vertical movement are controlled by a burner group movement control device 18 are used to vary the rotation speed of the soot body 12 based on the outer diameter of the soot body 12 that varies during growth, thereby controlling the rotation peripheral speed of the soot body 12 to be practically constant, and under conditions set such that the frequency coefficient γ calculated by the above formula (1) is 0.13 or more and less than 1.0, glass particles generated by a hydrolysis reaction caused by the flame of a glass particle synthesis burner 16a to which a glass raw material ( _SiCl4, etc.) is supplied are deposited on the outer surface of the rod-shaped target 14 whose rotation speed is controlled and held by the target holding and rotating mechanism 20 to grow the soot body 12, and then the target 14 is extracted from the soot body 12, thereby producing the hollow porous quartz glass base material of the present invention.

The cause of cracks is local density differences that occur within the soot body, which occur when the timing of one rotation of the soot body and the timing of the burner swing turn coincide. Now consider the case where Y rotations are made during X swings (X/2 round trips). The time required to swing X times is X(L/S), and conversely, the time required to rotate Y times is Y/N. Here, L is the burner travel distance (mm), S is the burner travel speed (mm/min), and N is the soot body rotation speed (rpm). The timing of the swing and rotation coincide, so X(L/S) = Y/N, and X/Y = S/(LN). This X/Y is called the frequency coefficient γ. γ shown in Figure 5 is the frequency coefficient.

For example, if two rotations occur during two swings, then γ = X/Y = 2/2 = 1. In this case, the timing of the rotation and swing will match at the left end of the swing during one turn, and the timing will match at the right end during the next turn. Since multiple burners are placed at equal intervals, the rotation and swing will match every turn, taking into account adjacent burners. The areas where they match will have a high density, while areas where they do not will have an extremely low density. This large density difference will cause cracks to appear during growth or after growth has finished.
In the present invention, by controlling the surface speed of the soot body to be substantially constant and setting γ to less than 1.0 in the range in which the outer diameter of the soot body exceeds 250 mm, a large hollow porous quartz glass preform free from cracks and ruptures can be obtained. In the present invention, the surface speed of the soot body is preferably 5 to 50 m/min, more preferably 5 to 10 m/min.

Furthermore, using the same concept, even if not every time, the rotation and the turnaround may coincide, and this also has an effect. Table 1 shows the frequency with which the rotation and the swing coincide when swing X=2 and rotation Y is an even number, and Table 2 shows the frequency with which the rotation and the swing coincide when swing X=2 and rotation Y is an odd number.

In the case of γ = 2/3 = 0.667, where there are three rotations during two swings (one round trip), the turning point of the swing coincides with the turning point of one rotation once every three rotations, resulting in a density difference, although it is minor compared to when they coincide every time. In the case of γ = 2/4 = 0.5, where there are four rotations during two swings (one round trip), the turning point of the swing coincides with the turning point of one rotation twice every four rotations, resulting in a density difference. As the density difference is not as great as when they coincide every time, cracks are unlikely to occur, but the density difference causes the distribution of chlorine concentration and OH group concentration to become non-uniform, making it impossible to obtain optically homogeneous quartz glass.

Therefore, by setting the swing distance, swing speed, and rotation speed so that the value of the frequency coefficient γ when N is at its minimum value _Nm in the frequency coefficient γ expressed by X/Y=S/(LN) is γ≦0.3, it is possible to achieve a condition in which the timing of the rotation and the swing do not coincide, and as a result, a quartz glass cylinder without cracks and with a small chlorine concentration distribution and OH group concentration distribution can be obtained. Since the present invention controls the rotational peripheral speed of the soot body to be practically constant, the rotational speed of the soot body decreases as the soot body grows. Therefore, in the present invention, the frequency coefficient γ is defined by the frequency coefficient γ when the rotation speed N is at its minimum value _Nm .

Furthermore, by setting the frequency coefficient γ to 0.13 or more, a soot body can be produced without causing vibration of the growing soot body or vibration of the apparatus even when deposition is performed with an outer diameter exceeding 250 mm.
In the present invention, the frequency coefficient γ is 0.13 or more and less than 1.0, and more preferably 0.13 or more and 0.3 or less. By making γ less than 1.0, cracks and ruptures of the soot body are eliminated, and by making γ 0.3 or less, it is possible to obtain a quartz glass cylinder that is free of cracks and ruptures of the soot body, has a uniform distribution of the chlorine concentration and the OH group concentration, and is optically and thermally homogeneous.

In the method of the present invention, the swing turning position may be moved in a fixed direction by a predetermined distance (α) and then moved in the opposite direction at a predetermined position, so-called wobbling conditions, or non-wobbling conditions may be used. Figure 2 is a schematic diagram showing the movement of the burner in the manufacturing method of the hollow porous quartz glass base material of the present invention, where (a) shows non-wobbling conditions and (b) shows wobbling conditions. In Figure 2, L is the swing distance, b is the burner spacing, and α is the wobbling shift amount. Note that Figure 2 shows the case where the swing distance and burner spacing are the same, but in the present invention, the swing distance and burner spacing may be the same or different.

When wobbling is performed, it is preferable to set the amount of movement α of the turning position during one round trip of the burner so that it falls within the range of formula (2) above when it is less than 1/3 of the flame diameter of the burner irradiated to the soot body. In the method of the present invention, by performing wobbling under the above conditions, it is possible to obtain a homogeneous hollow porous quartz glass base material with an extremely small amount of density fluctuation. Note that under wobbling conditions, if the amount of movement of the turning position exceeds 1/3 of the flame diameter, the turning positions are dispersed, so heat is also dispersed, and problems such as cracks and non-uniform physical properties are relatively unlikely to occur.

Figure 3 is a schematic diagram showing the irradiation of a burner in the manufacturing method of a hollow porous quartz glass base material of the present invention, where d is the flame irradiation diameter. Even when wobbling is used, if the amount of movement α of the turning position in each swing is 1/3 or less of the flame irradiation diameter d irradiated from the burner to the deposit and spreads, the overlap between layers is large, so the method of the present invention is effective. The flame irradiation diameter d can be measured by image analysis of the flame during soot body growth.

The method of the present invention can obtain a large hollow porous quartz glass preform with an outer diameter of more than 300 mm, which has small density fluctuations and is free of cracks and ruptures. Specifically, it can obtain a large hollow porous quartz glass preform with an outer diameter of more than 300 mm and an axial length of 2 m or more, and a large hollow porous quartz glass preform with an outer diameter of 500 mm or more and an axial length of 1.0 m or more. In addition, the method of the present invention can obtain a large hollow porous quartz glass preform with a weight of 100 kg or more. Furthermore, the method of the present invention can make it extremely easy to extract the target even if the soot body is large in diameter and heavy.

A first embodiment of the hollow porous quartz glass base material of the present invention is a large hollow porous quartz glass base material having an average density of the entire base material of 0.55 g/ ^cm3 or more, small density fluctuation, no cracks, an outer diameter of more than 300 mm, and a length of 2 m or more.
A second embodiment of the hollow porous quartz glass base material of the present invention is a large hollow porous quartz glass base material having an average density of the entire base material of 0.55 g/ ^cm3 or more, small density fluctuation, no cracks, and an outer diameter of 500 mm or more and a length of 1.0 m or more.

In the first and second aspects of the hollow porous quartz glass base material, the average density of the entire base material is 0.55 g/cm3 or ^more , preferably 0.56 g/cm3 or ^more and 0.77 g/cm3 or ^less , and more preferably 0.59 g/ ^cm3 or more and 0.68 g/cm3 or ^less .

Fig. 6 is a schematic diagram showing a method for measuring density variation in the hollow porous quartz glass preform of the present invention. As shown in Fig. 6, the density per cm3 is measured at four points (a to d) at equal distances (X mm) from the inner surface in the radial direction on four perpendicular lines (A to D) in four directions every 90° of the cylindrical cross section of the hollow porous quartz glass preform ¹² of the present invention, and the density variation is defined as the difference between the maximum and minimum density values of the four points (a to d). The density variation per unit length of the hollow porous quartz glass preform 12 of the present invention is 10%/cm or less, preferably 5%/cm or less, and more preferably 2%/cm or less, relative to the average value of the four points (a to d) in the four directions (A to D).

The third aspect of the hollow porous quartz glass preform of the present invention is a hollow porous quartz glass preform in which the density variation per unit length at four points equidistant from the inner surface in the radial direction in four directions every 90° on the cylindrical cross section is 2%/cm or less relative to the average value of the four points. In the method for producing the hollow porous quartz glass preform, the hollow porous quartz glass preform is produced under wobbling conditions in which the movement amount of the turning position in one round trip of the burner is 1/3 or less of the flame diameter of the burner irradiated to the soot body, and thus a homogeneous hollow porous quartz glass preform can be obtained with the aforementioned density variation being extremely small at 2%/cm or less.

The method for producing a synthetic quartz glass cylinder of the present invention uses a hollow porous quartz glass base material obtained by the method of the present invention. The method for producing the synthetic quartz glass cylinder is not particularly limited as long as the hollow porous quartz glass base material is used to produce a synthetic quartz glass cylinder by a known method, but a method of obtaining a synthetic quartz glass cylinder by dehydration treatment and sintering and vitrification, or a method of obtaining a synthetic quartz glass cylinder by pre-sintering and vitrification, is preferable. The method of the present invention can suitably produce a large synthetic quartz glass cylinder with an outer diameter of 200 mm or more that does not include any external defects caused by cracks in the porous member, is free of cracks and ruptures, and has a diameter of 200 mm or more.

Specifically, as the large synthetic quartz glass cylinder, a hollow synthetic quartz glass cylinder with an outer diameter of 200 mm or more can be obtained by using a cylindrical large hollow porous quartz glass base material with an outer diameter of more than 300 mm, and a hollow synthetic quartz glass cylinder with an outer diameter of 300 mm or more can be obtained by using a cylindrical large hollow porous quartz glass base material with an outer diameter of 500 mm or more. In particular, hollow synthetic quartz glass cylinders with an outer diameter of 200 mm or more but less than 300 mm and an axial length of 2.3 mm or more, and hollow synthetic quartz glass cylinders with an outer diameter of 300 mm or more and an axial length of 0.7 mm or more are more suitable.

In the present invention, by using a hollow porous quartz glass base material obtained under conditions in which γ is set to less than 1.0 in the range in which the outer diameter of the soot body exceeds 250 mm, a large quartz glass cylinder that does not contain any defective appearance caused by cracks in the porous member and is free of cracks and ruptures can be easily obtained. This quartz glass cylinder is particularly suitable as a material for semiconductor manufacturing jigs, where large sizes are desired. Furthermore, by using a hollow porous quartz glass base material obtained under conditions in which γ is set to 0.3 or less, a quartz glass cylinder that is free of cracks and ruptures, has a uniform distribution of chlorine concentration and OH group concentration, and is extremely homogeneous optically and thermally.

The first aspect of the hollow synthetic quartz glass cylinder of the present invention is a hollow synthetic quartz glass cylinder with an outer diameter of 200 to 500 mm and a length of 0.7 to 3.5 m, which is obtained by dehydrating and vitrifying the large hollow porous quartz glass base material by chlorine treatment, and which is characterized by having an OH group concentration of less than 5 ppm, a chlorine content concentration of 500 ppm to 3000 ppm, preferably 1000 ppm to 2500 ppm, and no external appearance defects caused by cracks in the porous member.

In the first embodiment of the hollow synthetic quartz glass cylinder, the "maximum-minimum difference" of the chlorine concentration at four positions equidistant from the inner surface of the cylindrical cross section of the hollow synthetic quartz glass cylinder, spaced every 90° in the circumferential direction, is preferably within 15% of the average value of the four positions, and more preferably within 10%.

The second aspect of the synthetic quartz glass cylinder of the present invention is a hollow synthetic quartz glass cylinder with an outer diameter of 200 to 500 mm and a length of 0.7 to 3.5 m, obtained by pre-sintering and vitrifying the large hollow porous quartz glass base material without chlorine treatment, characterized in that the OH group concentration is 50 ppm to 500 ppm, preferably 100 ppm to 300 ppm, and does not contain any external appearance defects caused by cracks in the porous member.

In the second embodiment of the hollow synthetic quartz glass cylinder, the "maximum-minimum difference" of the OH group concentration at four positions equidistant from the inner surface of the cylindrical cross section of the hollow synthetic quartz glass cylinder, spaced every 90° in the circumferential direction, is preferably within 15% of the average value of the four positions, and more preferably within 10%.

A third embodiment of the synthetic quartz glass cylinder of the present invention is a hollow synthetic quartz glass cylinder obtained by vitrifying the third embodiment of the hollow porous quartz glass base material, characterized in that the "difference between maximum and minimum values" of chlorine concentration at four positions equidistant from the inner surface of the cylindrical cross section of the hollow synthetic quartz glass cylinder and spaced every 90° in the circumferential direction is 10% or less of the average value of the four positions. The OH group concentration of the synthetic quartz glass cylinder is preferably less than 5 ppm, and more preferably contains substantially no OH groups. Incidentally, "substantially does not contain OH groups" means that the content of OH groups in the synthetic quartz glass cylinder is 0 ppm or more and less than 1 ppm.
The method for vitrifying the hollow porous quartz glass base material is not particularly limited, and any known method can be used, but a method in which the base material is dehydrated and sintered to obtain a synthetic quartz glass cylinder is preferred, and a method in which the base material is dehydrated in a chlorine atmosphere and then sintered to obtain a synthetic quartz glass cylinder is more preferred.

A fourth embodiment of the synthetic quartz glass cylinder of the present invention is a hollow synthetic quartz glass cylinder obtained by vitrifying the hollow porous quartz glass base material of the third embodiment, characterized in that the "difference between maximum and minimum values" of OH group concentrations at four positions equidistant from the inner surface of the cylindrical cross section of the hollow synthetic quartz glass cylinder and spaced every 90° in the circumferential direction is 10% or less of the average value of the four positions. It is preferable that the synthetic quartz glass cylinder is substantially free of chlorine. Note that "substantially free of chlorine" means that the chlorine content in the synthetic quartz glass cylinder is 0 ppm or more and less than 20 ppm.
The method for vitrifying the hollow porous quartz glass base material is not particularly limited, and any known method can be used, but a method in which the base material is dehydrated and sintered into a synthetic quartz glass cylinder, or a method in which the base material is pre-sintered and vitrified into a synthetic quartz glass cylinder is preferred, and a method in which the base material is dehydrated by heating without being chlorinated, and then sintered into a synthetic quartz glass cylinder is more preferred.

Conventionally, when the size was increased and the rotation conditions were set to be low in order to keep the peripheral speed constant during soot body growth, there was a problem that if dehydration treatment was performed in a chlorine atmosphere during the manufacture of a synthetic quartz glass cylinder, the chlorine content concentration distribution in the circumferential direction of the synthetic quartz glass cylinder became non-uniform, and if dehydration was performed by heating without chlorine treatment, the OH group content concentration distribution in the circumferential direction of the synthetic quartz glass cylinder became non-uniform. However, in the method of the present invention, by using a hollow porous quartz glass base material obtained under conditions in which the γ is set to 0.3 or less, it is possible to obtain an extremely homogeneous synthetic quartz glass cylinder in which the chlorine content concentration distribution is small even when dehydration treatment is performed in a chlorine atmosphere, and the difference in the OH group content concentration distribution is small even when dehydration is performed by heating without chlorine treatment.

Such extremely homogeneous synthetic quartz glass cylinders are particularly suitable as materials for optics and optical fibers, as well as for quartz glass jigs and lamps used in semiconductor manufacturing equipment. In particular, it was found that if the difference between the maximum and minimum values of the chlorine concentration distribution at each of the four circumferential points inside the cylinder cross section is within 15% of the average value of the four points, there is no effect on the characteristics of the optical fiber, including fiber curl.

The chlorine content distribution of a synthetic quartz glass cylinder that has been dehydrated and sintered to transparency in a chlorine atmosphere is preferably such that the difference between high and low concentrations in the four circumferential directions of the cylinder is 300 ppm or less, and more preferably 200 ppm or less.

In the distribution of OH group concentrations in a synthetic quartz glass cylinder that has been dehydrated by heating without chlorine treatment, the difference between the high and low OH group concentrations in the four circumferential directions of the cylinder is preferably 50 ppm or less, and more preferably 25 ppm or less.

Example 1
In the so-called OVD method, in which a plurality of burners for synthesizing glass particles are arranged at regular intervals, a row of burners is moved back and forth (swinged) relative to a rotating target [ceramic tube with an outer diameter (OD) of 50 mm], glass particles are deposited in layers on the target, and a glass particle deposit body is manufactured, a soot body is manufactured under the conditions of a burner interval of 100 mm, a swing distance L of 100 mm, a swing speed S of 140 mm/min (constant), and a surface peripheral speed of 11 m/min (constant), and the target is extracted from the soot body to obtain a hollow porous quartz glass base material. The manufacturing conditions are shown in Table 3, the results of the obtained hollow porous quartz glass base material are shown in Table 4, and the measurement results of the synthetic quartz glass cylinder are shown in Tables 5 and 6, respectively.

When the soot body is grown from a target OD of 50 mm to an outer diameter (OD) of 400 mm, the rotation speed is slowed down from 70.1 rpm to 8.8 rpm under the above conditions. The minimum rotation speed _Nm at that time is 8.8 rpm, and γ=S/(L· _Nm )=0.16.
As a result, although there was slight vibration during growth of the apparatus, growth proceeded without any problems, and there were no cracks in the soot body. A large hollow porous quartz glass preform (soot body) with an outer diameter of 400 mm, a total axial length of 3,500 mm, and a weight of 247 kg was successfully produced.

The average density and density variation of the entire soot body obtained were measured. The density variation was calculated by calculating the density per unit length at four points (a to d) at X = 105 mm in Figure 6, and the difference between the maximum and minimum density values at the four points (a to d) was defined as the density variation amount, and the ratio to the average value of the four points was calculated.

The average density of the entire soot body was 0.57 g/ ^cm3 , and the density variation per unit length at four points 105 mm from the inner surface in four directions was 4.4%/cm relative to the average value of the four points, resulting in a hollow porous quartz glass base material with an extremely small density variation.

The obtained hollow porous quartz glass base material was dehydrated and sintered to make it transparent in a chlorine atmosphere to obtain a synthetic quartz glass cylinder with an outer diameter of 210 mm, an inner diameter of 45 mm or less, and a length of 3.4 m. The obtained synthetic quartz glass cylinder had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The chlorine concentration was measured in each of the four directions by fluorescent X-ray analysis. The analytical device used for measuring the chlorine concentration was a fluorescent X-ray analyzer SPECTRO MIDEX manufactured by Spectro (lower detection limit of the device: chlorine concentration 20 ppm). The OH group concentration (OH group) was measured by FT-IR analysis. The analytical device used for measuring the OH group concentration was a Fourier transform infrared spectrometer Nicolet iS10 FT-IR manufactured by Thermo Fisher Scientific (lower detection limit of the device: OH group concentration 1 ppm). The fluctuation of the chlorine concentration was measured by measuring the difference between the maximum and minimum values of the chlorine concentration at four positions 50 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and the ratio to the average value of the four points was calculated. The results are shown in Table 5.

The chlorine concentration was measured in four circumferential directions on the cylinder, and was found to be between 1540 and 1720 ppm. The difference between the four directions was small, at a maximum of 180 ppm, and the variation from the average value of the four directions was a homogeneous 10.9%. Additionally, the OH group concentration (OH group) was less than 1 ppm.

Furthermore, a soot body prepared under the same conditions was dehydrated by heating without chlorine treatment, and then sintered and clarified to obtain a synthetic quartz glass cylinder having an outer diameter of 210 mm, an inner diameter of 45 mm or less, and a length of 3.4 m. The synthetic quartz glass cylinder obtained had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the OH group concentration was measured by measuring the difference between the maximum and minimum values of the OH group concentration at four positions 50 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value of the four points. The results are shown in Table 6.

When the OH group concentration was measured in four directions around the cylinder, it was found to be 230-255 ppm, with a small difference between the four directions of 25 ppm at most, and a homogeneous variation of 10.2% from the average value of the four directions. The chlorine concentration was also less than 20 ppm.

Example 2
A hollow porous quartz glass preform was obtained in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in Table 3. That is, a soot body was manufactured under the conditions of a burner interval of 100 mm, a swing distance L of 100 mm, a swing speed S of 200 mm/min (constant), and a surface peripheral speed of 9 m/min (constant), and the target was extracted from the soot body to obtain a hollow porous quartz glass preform. The results of the obtained hollow porous quartz glass preform are shown in Table 4, and the measurement results of the synthetic quartz glass cylinder are shown in Tables 5 and 6, respectively.

When the soot body is grown from an OD of 50 mm to an OD of 400 mm, the rotation speed is slowed down from 57.3 rpm to 7.2 rpm under the above conditions. The minimum rotation speed _Nm at that time is 7.2 rpm, and γ=0.28.
As a result, the growth was possible without any vibration of the apparatus during growth, there were no cracks in the soot body, and a large hollow porous quartz glass preform having an outer diameter of 400 mm, a total length of 3500 mm, and a weight of 247 kg could be produced.

The average density and density variation of the entire soot body obtained were measured. The density variation was calculated as the density per unit length at four points of X=105 mm in Fig. 6. The average density of the entire soot body was 0.57 g/ ^cm3 , and the density variation per unit length at a position 105 mm from the inner surface in four directions was 3.8%/cm with respect to the average value of the four points, and a hollow porous quartz glass base material with an extremely small density variation was obtained.

The obtained hollow porous quartz glass base material was dehydrated and sintered to make it transparent in a chlorine atmosphere to obtain a synthetic quartz glass cylinder with an outer diameter of 210 mm, an inner diameter of 45 mm or less, and a length of 3.4 m. The obtained synthetic quartz glass cylinder had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the chlorine concentration was measured by measuring the difference between the maximum and minimum values of the chlorine concentration at four positions 50 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value of the four points.
The chlorine concentration was measured in four circumferential directions of the cylinder, and the chlorine concentration was 1740 to 1960 ppm. The difference between the four directions was small, at a maximum of 220 ppm, and the variation from the average value of the four directions was 11.7%, indicating a homogeneous concentration. The OH group concentration (OH group) was less than 1 ppm.

Furthermore, a soot body prepared under the same conditions was dehydrated by heating without chlorine treatment, and then sintered and clarified to obtain a synthetic quartz glass cylinder having an outer diameter of 210 mm, an inner diameter of 45 mm or less, and a length of 3.4 m. The synthetic quartz glass cylinder obtained had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the OH group concentration was measured by measuring the difference between the maximum and minimum values of the OH group concentration at four positions 50 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value of the four points.
When the OH group concentration was measured in four directions around the cylinder, it was found that the OH group concentration was 225 to 255 ppm, the difference between the four directions was small at a maximum of 30 ppm, and the variation from the average value of the four directions was also homogeneous at 12.4%. The chlorine concentration was less than 20 ppm.

Example 3
A hollow porous quartz glass preform was obtained in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in Table 3. That is, a soot body was manufactured under the conditions of a burner interval of 100 mm, a swing distance L of 100 mm, a swing speed S of 600 mm/min (constant), and a surface peripheral speed of 9 m/min (constant), and the target was extracted from the soot body to obtain a hollow porous quartz glass preform. The results of the obtained hollow porous quartz glass preform are shown in Table 4, and the measurement results of the synthetic quartz glass cylinder are shown in Table 5.

When the soot body is grown from an OD of 50 mm to an OD of 400 mm, the rotation speed is slowed down from 57.3 rpm to 7.2 rpm under the above conditions. The minimum rotation speed _Nm at that time is 7.2 rpm, and γ=0.84.
As a result, the growth was possible without any vibration of the apparatus during growth, there were no cracks in the soot body, and a large hollow porous quartz glass preform having an outer diameter of 400 mm, a total length of 3500 mm, and a weight of 247 kg could be produced.

The average density and density variation of the entire soot body obtained were measured. The density variation was calculated as the density per unit length at four points of X=105 mm in Fig. 6. The average density of the entire soot body was 0.57 g/ ^cm3 , and the density variation per unit length at a position 105 mm from the inner surface in four directions was 9.5%/cm with respect to the average value of the four points.

The obtained hollow porous quartz glass base material was dehydrated and sintered to make it transparent in a chlorine atmosphere to obtain a synthetic quartz glass cylinder with an outer diameter of 210 mm, an inner diameter of 45 mm or less, and a length of 3.4 m. The obtained synthetic quartz glass cylinder had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the chlorine concentration was measured by measuring the difference between the maximum and minimum values of the chlorine concentration at four positions 50 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value.
The chlorine concentration was measured in four circumferential directions of the cylinder, and the chlorine concentration was 1640 to 2330 ppm. The difference between the four directions was as large as 690 ppm, and the amount of variation from the average value of the four directions was 34.9%, which indicated a decrease in homogeneity compared to Examples 1 and 2. The OH group concentration (OH group) was less than 1 ppm.

Furthermore, a soot body prepared under the same conditions was dehydrated by heating without chlorine treatment, and then sintered and clarified to obtain a synthetic quartz glass cylinder having an outer diameter of 210 mm, an inner diameter of 45 mm or less, and a length of 3.4 m. The synthetic quartz glass cylinder obtained had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the OH group concentration was measured by measuring the difference between the maximum and minimum values of the OH group concentration at four positions 50 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value.
When the OH group concentration was measured in four directions in the circumferential direction of the cylinder, the OH group concentration was 195 to 255 ppm, and the difference between the four directions was also large at a maximum of 60 ppm, and the amount of variation from the average value of the four directions was 26.7%, indicating that the homogeneity was lower than in Examples 1 and 2. In addition, the chlorine concentration was less than 20 ppm.

Example 4
A hollow porous quartz glass preform was obtained in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in Table 3. That is, a soot body was manufactured under the conditions of a burner interval of 100 mm, a swing distance L of 100 mm, a swing speed S of 200 mm/min (constant), a surface peripheral speed of 9 m/min (constant), and a wobbling shift amount α of 4 mm per swing (the flame irradiation diameter at this time was 28 mm, so the wobbling shift amount was 1/7 of the flame irradiation diameter. The flame diameter was measured by image analysis of the flame during the growth of the soot body). The target was extracted from the soot body to obtain a hollow porous quartz glass preform. The results of the obtained hollow porous quartz glass preform are shown in Table 4, and the results of the measurement of the synthetic quartz glass cylinder are shown in Table 5.

When the soot body is grown from an OD of 50 mm to an OD of 400 mm, the rotation speed is slowed down from 57.3 rpm to 7.2 rpm under the above conditions. The minimum rotation speed _Nm at that time is 7.2 rpm, and γ=0.28.
As a result, the growth was possible without any vibration of the apparatus during growth, there were no cracks in the soot body, and a large hollow porous quartz glass preform having an outer diameter of 400 mm, a total length of 3500 mm, and a weight of 247 kg could be produced.
The average density and density variation of the entire soot body obtained were measured. The density variation was calculated as the density per unit length at four points of X = 105 mm in Figure 6. The average density of the entire soot body was 0.57 g / cm ³ , and the density variation per unit length at a position 105 mm from the inner surface in four directions was 1.6% / cm with respect to the average value of the four points, and a hollow porous quartz glass base material with an extremely small density variation was obtained.

The obtained hollow porous quartz glass base material was dehydrated and sintered to make it transparent in a chlorine atmosphere to obtain a synthetic quartz glass cylinder with an outer diameter of 210 mm, an inner diameter of 45 mm or less, and a length of 3.4 m. The obtained synthetic quartz glass cylinder had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the chlorine concentration was measured by measuring the difference between the maximum and minimum values of the chlorine concentration at four positions 50 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value of the four points.
The chlorine concentration was measured in four circumferential directions of the cylinder, and the chlorine concentration was 1860 to 1995 ppm. The difference between the four directions was extremely small, at a maximum of 135 ppm, and the variation from the average value of the four directions was 6.9%, indicating a homogeneous concentration. The OH group concentration (OH group) was less than 1 ppm.

Furthermore, a soot body prepared under the same conditions was dehydrated by heating without chlorine treatment, and then sintered and clarified to obtain a synthetic quartz glass cylinder having an outer diameter of 210 mm, an inner diameter of 45 mm or less, and a length of 3.4 m. The synthetic quartz glass cylinder obtained had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the OH group concentration was measured by measuring the difference between the maximum and minimum values of the OH group concentration at four positions 50 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value of the four points.
When the OH group concentration was measured in four directions around the cylinder, it was found that the OH group concentration was 200 to 215 ppm, the difference between the four directions was small at a maximum of 15 ppm, and the variation from the average value of the four directions was also homogeneous at 7.1%. The chlorine concentration was less than 20 ppm.

Example 5
A hollow porous quartz glass preform was obtained in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in Table 3. That is, a soot body was manufactured under the conditions of a burner interval of 100 mm, a swing distance L of 100 mm, a swing speed S of 200 mm/min (constant), and a surface peripheral speed of 13 m/min (constant), and the target was extracted from the soot body to obtain a hollow porous quartz glass preform. The results of the obtained hollow porous quartz glass preform are shown in Table 4, and the measurement results of the synthetic quartz glass cylinder are shown in Table 5.

When the soot body is grown from an OD of 50 mm to an OD of 600 mm, the rotation speed is slowed down from 82.8 rpm to 6.9 rpm under the above conditions. The minimum rotation speed _Nm at that time is 6.9 rpm, and γ=0.29.
As a result, the growth was possible without any vibration of the apparatus during growth, there were no cracks in the soot body, and a large hollow porous quartz glass preform having an outer diameter of 600 mm, a total length of 2500 mm and a weight of 402 kg was produced.
The average density and density variation of the entire soot body obtained were measured. The density variation was calculated as the density per unit length at four points of X=200 mm in Fig. 6. The average density of the entire soot body was 0.57 g/ ^cm3 , and the density variation per unit length at a position 200 mm from the inner surface in four directions was 3.7%/cm with respect to the average value of the four points, and a hollow porous quartz glass base material with an extremely small density variation was obtained.

The obtained hollow porous quartz glass base material was dehydrated and sintered to make it transparent in a chlorine atmosphere to obtain a synthetic quartz glass cylinder with an outer diameter of 350 mm, an inner diameter of 45 mm or less, and a length of 1.9 m. The obtained synthetic quartz glass cylinder had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the chlorine concentration was measured by measuring the difference between the maximum and minimum values of the chlorine concentration at four positions 100 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value of the four points.
The chlorine concentration was measured in four circumferential directions of the cylinder, and the chlorine concentration was 1890 to 2170 ppm. The difference between the four directions was small, at a maximum of 280 ppm, and the variation from the average value of the four directions was 14.1%, indicating a homogeneous concentration. The OH group concentration (OH group) was less than 1 ppm.

Furthermore, a soot body prepared under the same conditions was dehydrated by heating without chlorine treatment, and then sintered and clarified to obtain a synthetic quartz glass cylinder having an outer diameter of 350 mm, an inner diameter of 45 mm or less, and a length of 1.9 m. The synthetic quartz glass cylinder obtained had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the OH group concentration was measured by measuring the difference between the maximum and minimum values of the OH group concentration at four positions 50 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value of the four points.
When the OH group concentration was measured in four directions around the cylinder, it was found that the OH group concentration was 225 to 245 ppm, the difference between the four directions was also small at a maximum of 25 ppm, and the variation from the average value of the four directions was also homogeneous at 10.5%. In addition, the chlorine concentration was less than 20 ppm.

Example 6
A hollow porous quartz glass preform was obtained in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in Table 3. That is, a soot body was manufactured under the conditions of a burner interval of 100 mm, a swing distance L of 100 mm, a swing speed S of 400 mm/min (constant), and a surface peripheral speed of 9 m/min (constant), and the target was extracted from the soot body to obtain a hollow porous quartz glass preform. The results of the obtained hollow porous quartz glass preform are shown in Table 4, and the measurement results of the synthetic quartz glass cylinder are shown in Table 5.

When the soot body is grown from an OD of 50 mm to an OD of 600 mm, the rotation speed is slowed down from 57.3 rpm to 4.8 rpm under the above conditions. The minimum rotation speed _Nm at that time is 4.8 rpm, and γ=0.84.
As a result, the growth was possible without any vibration of the apparatus during growth, there were no cracks in the soot body, and a large hollow porous quartz glass preform having an outer diameter of 600 mm, a total length of 2500 mm and a weight of 402 kg was produced.
The average density and density variation of the entire soot body obtained were measured. The density variation was calculated as the density per unit length at four points of X=200 mm in Fig. 6. The average density of the entire soot body was 0.57 g/ ^cm3 , and the density variation per unit length at a position 200 mm from the inner surface in four directions was 8.3%/cm with respect to the average value of the four points.

The obtained hollow porous quartz glass base material was dehydrated and sintered to make it transparent in a chlorine atmosphere to obtain a synthetic quartz glass cylinder with an outer diameter of 350 mm, an inner diameter of 45 mm or less, and a length of 1.9 m. The obtained synthetic quartz glass cylinder had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the chlorine concentration was measured by measuring the difference between the maximum and minimum values of the chlorine concentration at four positions 100 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value of the four points.
The chlorine concentration was measured in four circumferential directions of the cylinder, and the chlorine concentration was 1725 to 2340 ppm. The difference in the four directions was as large as 615 ppm, and the amount of variation from the average value in the four directions was 29.1%, indicating that the homogeneity was lower than in Examples 4 and 5. The OH group concentration (OH group) was less than 1 ppm.

Furthermore, a soot body prepared under the same conditions was dehydrated by heating without chlorine treatment, and then sintered and clarified to obtain a synthetic quartz glass cylinder having an outer diameter of 350 mm, an inner diameter of 45 mm or less, and a length of 1.9 m. The synthetic quartz glass cylinder obtained had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the OH group concentration was measured by measuring the difference between the maximum and minimum values of the OH group concentration at four positions 50 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value of the four points.
When the OH group concentration was measured in four directions in the circumferential direction of the cylinder, the OH group concentration was 200 to 250 ppm, and the difference between the four directions was also relatively large at a maximum of 50 ppm, and the amount of variation from the average value of the four directions was 21.7%, indicating that the homogeneity was lower than in Examples 4 and 5. In addition, the chlorine concentration was less than 20 ppm.

(Example 7)
A hollow porous quartz glass preform was obtained in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in Table 3. That is, a soot body was manufactured under the conditions of a burner interval of 100 mm, a swing distance L of 100 mm, a swing speed S of 200 mm/min (constant), a surface peripheral speed of 13 m/min (constant), and a wobbling shift amount α of 4 mm per swing (the flame irradiation diameter at this time was 28 mm, so the wobbling shift amount was 1/7 of the flame irradiation diameter), and the target was extracted from the soot body to obtain a hollow porous quartz glass preform. The results of the obtained hollow porous quartz glass preform are shown in Table 4, and the measurement results of the synthetic quartz glass cylinder are shown in Table 5.

When the soot body is grown from an OD of 50 mm to an OD of 600 mm, the rotation speed is slowed down from 82.8 rpm to 6.9 rpm under the above conditions. The minimum rotation speed _Nm at that time is 6.9 rpm, and _γ = 0.29.
As a result, the growth was possible without any vibration of the apparatus during growth, there were no cracks in the soot body, and a large hollow porous quartz glass preform having an outer diameter of 600 mm, a total length of 2500 mm and a weight of 402 kg was produced.
The average density and density variation of the entire soot body obtained were measured. The density variation was calculated as the density per unit length at four points of X=200 mm in Fig. 6. The average density of the entire soot body was 0.57 g/ ^cm3 , and the density variation per unit length at a position 200 mm from the inner surface in four directions was 1.8%/cm with respect to the average value of the four points, and a hollow porous quartz glass base material with an extremely small density variation was obtained.

The obtained hollow porous quartz glass base material was dehydrated and sintered to make it transparent in a chlorine atmosphere to obtain a synthetic quartz glass cylinder with an outer diameter of 350 mm, an inner diameter of 45 mm or less, and a length of 1.9 m. The obtained synthetic quartz glass cylinder had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the chlorine concentration was measured by measuring the difference between the maximum and minimum values of the chlorine concentration at four positions 100 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value of the four points.
The chlorine concentration was measured in four circumferential directions of the cylinder, and the chlorine concentration was 1770 to 1935 ppm. The difference in the four directions was small, at a maximum of 165 ppm, and the variation from the average value of the four directions was 8.8%, indicating a homogeneous concentration. The OH group concentration (OH group) was less than 1 ppm.

Furthermore, a soot body prepared under the same conditions was dehydrated by heating without chlorine treatment, and then sintered and clarified to obtain a synthetic quartz glass cylinder having an outer diameter of 350 mm, an inner diameter of 45 mm or less, and a length of 1.9 m. The synthetic quartz glass cylinder obtained had a good appearance without any defects caused by cracks in the porous member.
The chlorine concentration and OH group concentration of the obtained quartz glass cylinder were measured. The fluctuation of the OH group concentration was measured by measuring the difference between the maximum and minimum values of the OH group concentration at four positions 50 mm from the inner surface of the cylindrical cross section at 90° intervals in the circumferential direction, and calculating the ratio to the average value of the four points.
When the OH group concentration was measured in four directions around the cylinder, it was found that the OH group concentration was 205 to 225 ppm, the difference in the four directions was also small at a maximum of 20 ppm, and the variation from the average value of the four directions was also homogeneous at 9.4%. In addition, the chlorine concentration was less than 20 ppm.

(Comparative Example 1)
A hollow porous quartz glass base material was manufactured in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in Table 3. That is, a soot body was manufactured under the conditions of a burner interval of 100 mm, a swing distance L of 100 mm, a swing speed S of 140 mm/min (constant), and a surface peripheral speed of 18 m/min (constant).

When growing the soot body from a target OD of 50 mm to an OD of 400 mm, under the above conditions, the rotation speed would be slowed down from 114.6 rpm to 14.3 rpm. However, when the soot body OD exceeded 200 mm, the device began to vibrate, and the vibrations became so strong when the soot body OD exceeded 250 mm, so production was stopped midway and it was not possible to continue production up to OD 400.

(Comparative Example 2)
A hollow porous quartz glass preform was manufactured in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in Table 3. That is, a soot body was manufactured under the conditions of a burner interval of 100 mm, a swing distance L of 100 mm, a swing speed S of 800 mm/min (constant), and a surface peripheral speed of 9 m/min (constant), and the target was extracted from the soot body to obtain a hollow porous quartz glass preform. The results of the obtained hollow porous quartz glass preform are shown in Table 4.

When the soot body is grown from a target OD of 50 mm to an OD of 400 mm, the rotation speed is slowed down from 57.3 rpm to 7.2 rpm under the above conditions. The minimum rotation speed _Nm at that time is 7.2 rpm, and γ is 1.12. As a result, the growth was possible without any vibration during the growth of the device, but when the soot body OD reached approximately 300 mm, a crack occurred in the soot body and production could not be continued.

(Comparative Example 3)
A hollow porous quartz glass preform was manufactured in the same manner as in Example 1, except that the manufacturing conditions were changed as shown in Table 3. That is, a soot body was manufactured under the conditions of a burner interval of 100 mm, a swing distance L of 100 mm, a swing speed S of 800 mm/min (constant), a surface peripheral speed of 9 m/min (constant), and a wobbling shift amount α of 4 mm per swing (the flame irradiation diameter at this time was 28 mm, so the wobbling shift amount was 1/7 of the flame irradiation diameter. The flame diameter was measured by image analysis of the flame during the growth of the soot body). The target was extracted from the soot body to obtain a hollow porous quartz glass preform. The results of the obtained hollow porous quartz glass preform are shown in Table 4.

When the soot body is grown from a target OD of 50 mm to an OD of 400 mm, the rotation speed is slowed down from 57.3 rpm to 7.2 rpm under the above conditions. The minimum rotation speed _Nm at that time is 7.2 rpm, and γ is 1.12. As a result, the growth was possible without any vibration during the growth of the device, but when the soot body OD reached approximately 350 mm, a crack occurred in the soot body and production could not be continued.

10: Manufacturing equipment, 12: Soot body, 14: Target, 16: Burner group for synthesizing glass particles, 16a: Burner for synthesizing glass particles, 18: Swing and vertical movement device for the burner group for synthesizing glass particles, 20: Target holding and rotation mechanism, 22: Burner flame, d: Flame irradiation diameter, L: Swing distance, b: Burner spacing, α: Wobbling shift amount.

Claims (13)

a step of arranging a plurality of burners for synthesizing glass particles at a predetermined interval, reciprocating the burners, and depositing glass particles on a rotating target to grow a soot body;
extracting the target from the soot body to produce a hollow porous quartz glass base material;
A method for producing a hollow porous quartz glass base material, comprising:
A method for producing a hollow porous quartz glass base material, characterized in that the rotational peripheral speed of the soot body is controlled to be virtually constant by varying the rotation speed of the soot body based on the outer diameter of the soot body which varies during growth, and the frequency coefficient γ calculated by the following formula (1) is set to be within the range of the following formula (2) in the range in which the outer diameter of the soot body exceeds 250 mm.
γ=S/(L・N _m )...(1)
0.13≦γ<1.0 (2)
[In the formula (1), S is the moving speed of the burner (mm/min), L is the moving distance of the burner (mm), and _Nm is the minimum value (rpm) of the fluctuating rotation speed of the soot body.] The method for manufacturing a hollow porous quartz glass base material according to claim 1, characterized in that the turning position in the reciprocating movement of the burner is moved by a predetermined distance, and the amount of movement of the turning position in one reciprocating movement of the burner is 1/3 or less of the flame diameter of the burner irradiated to the soot body. The method for manufacturing a hollow porous quartz glass base material according to claim 1 or 2, characterized in that the frequency coefficient γ is 0.13 or more and 0.3 or less. A method for manufacturing a synthetic quartz glass cylinder, characterized by using a hollow porous quartz glass base material obtained by the method according to any one of claims 1 to 3. A large, hollow, porous quartz glass preform having a cylindrical shape with an outer diameter exceeding 300 mm and a length of 2 m or more, characterized in that the average density of the entire preform is 0.55 g/cm3 ^or more , and when the density variation is defined as the difference between the maximum and minimum density values per ^cm3 at four points equidistant (X mm) from the inner surface in the radial direction on four perpendicular lines every 90° on the cross section of the cylinder, the density variation per unit length at a distance (X mm) from the inner surface is 10%/cm or less of the average value of the four points, and the preform contains no cracks. A large, hollow, porous quartz glass preform having a cylindrical shape with an outer diameter of 500 mm or more and a length of 1.0 m or more, characterized in that the average density of the entire preform is 0.55 g/ ^{cm3 or} more, and when the density variation is defined as the difference between the maximum and minimum density values per cm3 at four points equidistant (X mm) from the inner surface in the radial direction on four perpendicular lines in each 90° direction of the cylindrical cross section, the density variation per unit length at a distance (X mm) from the inner surface is 10%/cm or less of the average value of the four points, and the preform contains no cracks. 7. A hollow porous quartz glass base material according to claim 5 or 6, wherein the density variation per unit length at a distance (X mm) from the inner surface is 2 %/cm or less of the average value of the four points, when the density variation is defined as the difference between the maximum and minimum density per cm3 at four points equidistant ⁽ X mm) from the inner surface in the radial direction on four perpendicular lines in every 90° on the cylindrical cross section. A hollow synthetic quartz glass cylinder obtained by vitrifying the hollow porous quartz glass base material according to any one of claims 5 to 7 ,
A hollow synthetic quartz glass cylinder having an outer diameter of 200 to 500 mm, a length of 0.7 to 3.5 m, an OH group concentration of less than 5 ppm, a chlorine content concentration of 500 ppm to 3000 ppm , and no external defects. A hollow synthetic quartz glass cylinder according to claim 8, characterized in that the "difference between the maximum value and the minimum value" of the chlorine concentration at four positions every 90° in the circumferential direction, which are equidistant from the inner surface of the cylindrical cross section of the hollow synthetic quartz glass cylinder, is within 15% of the average value of the four positions. A hollow synthetic quartz glass cylinder obtained by vitrifying the hollow porous quartz glass base material according to any one of claims 5 to 7 ,
A hollow synthetic quartz glass cylinder having an outer diameter of 200 to 500 mm, a length of 0.7 to 3.5 m, an OH group concentration of 50 ppm to 500 ppm , and no external defects. A hollow synthetic quartz glass cylinder according to claim 10, characterized in that the "difference between maximum and minimum values" of OH group concentrations at four positions every 90° in the circumferential direction, equidistant from the inner surface of the cylindrical cross section of the hollow synthetic quartz glass cylinder, is within 15 % of the average value of the four positions. A hollow synthetic quartz glass cylinder obtained by vitrifying the hollow porous quartz glass base material according to claim 7 ,
A hollow synthetic quartz glass cylinder, characterized in that the "difference between the maximum value and the minimum value" of the chlorine concentration at four positions equidistant from the inner surface of the cylindrical cross section of the hollow synthetic quartz glass cylinder and spaced every 90° in the circumferential direction is 10% or less of the average value of the four positions. A hollow synthetic quartz glass cylinder obtained by vitrifying the hollow porous quartz glass base material according to claim 7 ,
A hollow synthetic quartz glass cylinder, characterized in that the "difference between maximum value and minimum value" of OH group concentration at four positions every 90° in the circumferential direction, which are equidistant from the inner surface of the cylindrical cross section of the hollow synthetic quartz glass cylinder, is 10% or less of the average value of the four positions.

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